pressure sensitive lines (drawing with iPad pencil)
In order to make this work, we start by capturing points from a mark.
We also capture a delta (the change between this point and the previous point), from which we can get a direction for each point. Here I'm drawing lines at each point with that point's direction rotated 90deg.
You can think of those lines as being between two points, which we make by moving the actual point by some "distance" in the cross direction of the line.
To make these responsive to pressure, we just need to make that "distance" be based on the pointer event's pressure. More pressure = more distance = thicker part of the line. (We could also use velocity rather than pressure!)
Finally, we need to connect the dots. We do this in order—connecting all the positive / blue dots until we get to the end, then connecting all the negative / yellow dots on our way back.
And that's our pressure sensitive stroke!
Plenty of potential improvements, such as using a cardinal spline to smooth out the line edges, or adding a rounded cap, but that's the general idea. Pretty cool, right?
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